That last comment is right. It's about how he cheated on her, or did something like that, early on in the relationship, when he thought it wouldn't matter if it ended. But as the relationship progressed, and they fell deeply in love, he became afraid that his former Sins would be discovered. Eventually they were, and when he walked in, she hit him with what he had done, Hence the Metaphorical feeling of being "Blown Wide Open" Which also explains why he cries out "Why's She Going?" at the end of the song, like he's saying "Goddamnit, I did it before, when I didn't think it'd matter, I realize I've done wrong and I think we can work through it."
That last comment is right. It's about how he cheated on her, or did something like that, early on in the relationship, when he thought it wouldn't matter if it ended. But as the relationship progressed, and they fell deeply in love, he became afraid that his former Sins would be discovered. Eventually they were, and when he walked in, she hit him with what he had done, Hence the Metaphorical feeling of being "Blown Wide Open" Which also explains why he cries out "Why's She Going?" at the end of the song, like he's saying "Goddamnit, I did it before, when I didn't think it'd matter, I realize I've done wrong and I think we can work through it."